In recent years, it has been desired to reduce emissions of greenhouse gases to prevent global warming. It is further required to reduce carbon dioxide (CO2) occupying a major part of greenhouse gases. Technological development for reduction of carbon dioxide is classified into three fields of improvement in energy conversion efficiency, exploration and development of new energy, and collection and sequestration of carbon dioxide.
Among these, regarding collection and sequestration of carbon dioxide, particularly research and development of a carbon dioxide-absorbing material that can efficiently absorb carbon dioxide has been recently carried out actively.
It has been found in research of fuel cells that regarding stabilization of ceramics in a molten carbonate, a lithium composite oxide and carbon dioxide are reacted to form an oxide and lithium carbonate. Non-Patent Document 1 describes the following contents. Lithium zirconate (Li2ZrO3) as a lithium composite oxide is reacted with carbon dioxide at the low temperature side of a boundary of about 700° C. and converted into zirconium oxide (ZrO2), and the zirconium oxide releases carbon dioxide at the high temperature side and reverts to lithium zirconate. It is further described that other than the lithium zirconate, lithium silicate (Li4SiO4) shows similar reaction behavior.
Non-Patent Document 2 and Non-Patent Document 3 describe a production example of lithium titanate (Li4TiO4) and that Li4TiO4 obtained by the production method has a high property for absorbing carbon dioxide.
However, according to experiments by the present inventors, the Li2ZrO3 described in Non-Patent Document 1 could only absorb carbon dioxide in an amount of 23% by mass with respect to 100 g of Li2ZrO3(S).
Furthermore, when the maximum absorption amount of carbon dioxide in the lithium silicate (Li4SiO4) described in Non-Patent Document 1 is theoretically obtained from the following chemical formula (1), the amount is 36.72% by mass.Li4SiO4+CO2→Li2SiO3+Li2CO3  Chemical formula (1)
When the maximum absorption amount of carbon dioxide in the Li4TiO4 described in Non-Patent Documents 2 and 3 is theoretically obtained from the following chemical formula (2), the amount is 31.55% by mass.Li4TiO4+CO2→Li2TiO3+Li2CO3  Chemical formula (2)
However, the Li4TiO4 obtained by the methods described in Non-Patent Documents 2 and 3 does not actually exhibit the theoretical maximum absorption amount of carbon dioxide, and the amount did not exceed about 21% by mass.
Non-Patent Document 1: Ceramics 37 (2002) No. 11
Non-Patent Document 2: B. L. Dubey and A. R. West, Nature Physical Science, vol. 235, Feb. 21, 1972
Non-Patent Document 3: R. P. Gunawardane, et al., J. Solid State Chem 112, 70-72 (1994)